The present invention relates to a system and methods for improving the performance of airflow energy harvesting techniques. In particular, where airflow is the result of some forced air application, as would be the case with a ventilation or heat exchange system or other fan driven air movement, installation costs may be reduced. This system and method may be of particular use in ventilation system utilized on animal housing, such as barn rooms for pig and poultry farming.
Animal farming requires significant ventilation of the animal housings. Modern pig buildings (and poultry buildings) are complex structures with a high need of environmental control. Many of the structures are tunnel ventilated. The ventilation system is a central part of the accommodation, which must be integrated with the building to achieve an acceptable living environment and to aid in bio-security and disease prevention. Open window type housing is inadequate and exposes the livestock to many communicable diseases brought in by other animals, birds or bats. Lack of control may lead to environmental failure and, as a consequence, abnormal behavior, such as tail biting, or disease problems might arise.
Ventilation systems are based on the principle that when cool outside air moves through a building, it warms and picks up moisture, provides circulation, oxygenates the enclosed housing and removes pollutants such as gases and dust. In warming, it removes heat from the building. In winter, the ventilation system is mainly used to control the moisture content of the air. Additional heat might be required to maintain the temperature of the controlled environment and to ensure that the humidity is controlled. The exhausted air contains considerably more energy than the cool air that entered the system.
Ventilation for an animal housing operates almost constantly and consumes large quantities of energy over the course of a year. This is a substantial component of the operating cost of a farm. By reducing ventilation energy costs, by improving efficiency and/or through energy harvesting or recapture, the operational costs of the farm may be dramatically reduced. This provides the farm with a commercial advantage over competitor farms, as well as reducing energy consumption, which aids the environment.
Currently a number of known methods for improving animal housing energy efficiency are employed. These include better insulation of housing buildings, fan systems optimized for efficiency, wind-tunnel type ventilation designs and methods which take advantage of convection and passive ventilation principles. However, despite these improvements in energy efficiency for animal farming, the constant usage of large scale fans is a major expenditure of energy.
Forced air movement is also commonplace throughout industrial and commercial premises. Ventilation systems, a routine part of environmental control systems, are also to be found throughout urban areas and, in general, the energy in the exhausted air is simply allowed to diffuse into the atmosphere. In some cases this process may be controlled to some extent to mitigate the noise footprint of the system. Typically, diffuser systems and plenum assemblies are added to the exhaust port so as to enable a smoother transition to ambient conditions. By controlling the flow, turbulence may be reduced which in turn may greatly reduce the noise produced.
Quite often, because it is being powered by a large, simple fan, an output airstream rotates in a spiral fashion and creates significant turbulence. This produces noise and there is usually a desire to reduce this. Ducting may be added to the outlet port so as to reduce or eliminate this rotation and flow straighteners may also be added. These are simple in design and sometimes crude, but generally operate so as to control costs and achieve acceptable results. Where a centrifugal fan is used, often referred to as a “squirrel cage blower,” the rotational energy is not usually significant but the base application is normally for systems where a substantial pressure gain is required. Typically these would be used to pressurize a duct system used for positive pressure ventilation.
Because there is considerable energy in the exhaust airflow, attention is being paid to efforts to extract some of this energy by using small wind powered generators in the airstream. The concerns about increasing the loading on the prime mover are well understood, though the problems of finding a good location point for the wind turbine have been a challenge. Empirical guidelines for keeping the wind turbine about a meter away from the primary exhaust fan helps ensure that there is no significant increase in back-pressure. In an attempt to make the airflow resemble natural winds, some installations make use of flow straightening techniques to ensure that the turbine sees something approaching the linear flow characteristics of a free airstream, especially where the driving fan is in close proximity to the outlet, but at the cost of complexity of the resulting assembly.
In cases where the energy recovery or harvesting is space constrained, flow straighteners may be impractical and other means must be employed to gain turbine efficiency in a machine generated airflow. In general, it is not desirable to make any modifications or attachments to the original ventilation or exhaust system to ensure that no warranty or liability concerns are created from the original installation.
It is therefore apparent that an urgent need exists for optimization of wind turbines located so as to harvest or scavenge energy from an air exhaust having a driving fan in close proximity to the outlet. This improved system enables a useful increase in efficiency, reduced dependence on ducting and flow straighteners and simplified installation.